Pre-cleaner units for cleaning air flowing into an internal combustion engine are known. These units remove coarse particles from the air flow by causing rotation of the air flow so that centrifugal force separates the coarse particles from the air flow. These particles are then collected in the pre-cleaner unit housing. U.S. Pat. Nos. 4,248,613 and 3,864,109 show air cleaners which are typical of this type.
Air filters for internal combustion engines having a means for removing accumulated debris which has been removed from air are known in the art. The filters shown in U.S. Pat. Nos. 3,877,454; 4,204,848; 3,696,591; 3,838,675; and Re. 30,409 have motor-driven vacuum pumps which remove accumulated debris from the filters. Each of these devices requires a separate power means for driving the vacuum pump.
Another type of apparatus which evacuates a cleaner unit is described in the Prior Art section of U.S. Pat. No. 4,248,613. There is described a unit wherein a venturi tube is attached to the exhaust pipe of an engine. The suction created by the venturi tube evacuates particles from a pre-cleaner unit which is connected to an internal combustion engine.
It is also known to employ an air filter in connection with an air conditioner which cools air admitted to the cab of a vehicle, particularly a farm tractor. Since air admitted to the cab contains a high concentration of dust, the filter frequently becomes clogged.